Chapter 6 - Active control of thermoacoustic instability

Abstract

Self-sustained combustion instabilities are one of the most plaguing challenges and problems in lean-conditioned propulsion systems, such as rocket motors, gas turbines, industrial furnace and boilers, and turbo-jet thrust augmenters. Either passive or active control in open- or closed-loop configurations can achieve it. One of the classical disadvantages of passive control is that it is only implementable to a designed combustor over a limited frequency range and can not respond to the changes in operating conditions. Compared with the passive control approaches, active control, especially in closed-loop configuration, is more adaptive and has inherent capacity to be implemented in practice. The key components in closed-loop active control are (1) sensor, (2) controller (optimization algorithm), and (3) dynamic actuator. This chapter outlines the current status, technical challenges, and development progress of the active control approaches (in open- or closed-loop configurations). A brief description of feedback control, adaptive control, model-based control, and sliding mode control are provided first by introducing a simplified Rijke-type combustion system. The modeled combustion system provides an invaluable platform to evaluate the performance of these feedback controllers and a transient growth controller. The performance of these controllers is compared and discussed. An outline of theoretical, numerical, and experimental investigations are then provided to overview the research and development progress made during the last few decades. Finally, the potential challenges and issues involved with the design, application, and implementation of active combustion control strategies on a practical engine system are highlighted.